Production of flexible tubes and pipes



Oct. 28 1941. w. H. GRINT 2,260,282

" PRODUCTION OF FLEXIBLE TUBES AND PIPES Fild Oct. 25, 1957 8Sheets-Sheet 1 ATTOP/VEYS Oct. 28, 1941, w. H. GRIN T PRODUCTION OFFLEXIBLE TUBES AND PIPES 8 Sheets-Sheet 2 Filed Oct. 23, 1937 //v VEN70R VIZ/r. 6 12/0 77 lfi l r l l vliliI Iillllllil'illllldlilillllIliIrIllll illlllalililll I: It!!! t u 20 20a 20 20 20a 20 ATTOR/VEXS Oct.28, 1941. w, H, GRI N T 2,260,222

PRODUCTION OF FLEXIBLE TUBES AND PIPES Filed Oct. 25, 1937 8Sheets-Sheet 3 Fig.4. 78 j 44 /J/ Oct. 28, 1941. w. H. 'GRlNT PRODUCTIONOF FLEXIBLE TUBES AND PIPES Filed Oct. 25, 1957 a Sheets-Sheet. 4

. l/vx twrofl 14 46. f rr BY; Arron/5m Oct. 28, 1941. w. H. GRINTPRODUCTION OF FLEXIBLE TUBES AND PIPES Filed Oct. 23, 1937 8Sheets-Sheet 5 Fig. 10.

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0a. 28, 1941. w, H, mm 2,260,282

PRODUCTION OF FLEXIBLE TUBES AND PIPES Filed Oct. 23, 1937 8Sheets-Sheet 6 i I i I a z i T I M i I; 46 5 Fig.14

Arrow/B Oct.28, 1941. w; RINT 2,260,282

PRODUCTION OF FLEXIBLE (TUBES AND PIPES Filed ootfzs', 1937 8Sheets-Sheet 7 Fig.16.

HTIDR/VEW Oct. 28, 1941. w. H. GRINT I 2,260,232

JEROIDUC'IION OF FLEXIBLE TUBES AND PIPES Filed 061;. 25, 1957 8Sheets-Sheet 8 which can be made'in former an Patented'Oct. 28, 1941UNITED STATES PATENT OFFICE PRODUCTION OF FLEXIBLE TUBES AND PIPESWilliam Horace Grint, Trading Estate, Slough, England ApplicationOctober 23, 193%, Serial No. 170,708 In Great Britain October so, 19%

1 Claim.

This invention relates to flexible tubes or pipes and to the manufacturethereof. I I

In order to provide a flexible tubeunaffected by the actionof petrol andoil, it has already' been proposed to make tubes of various materialsbore is preferable. Indeed, it has also been proposed to manufacturesuch smooth bore tubes by'dipping a mandrel several times in polyvinylalcohol or derivatives of polyvinyl alcohol so .as to build up a tubelayer by. layer on the mandrel. However, this method gives rise to.difliculties owing to which the bore and length of tubes this way arelimited, the chief difliculty being the removal ofthe tube from themandrel. I

One object of the invention consists in the method of manufacturing aflexible tube which includes the step of setting up such relativemovement between a. pre-formed flexible tubular former and a mass ofliquid medium that at least one surface .of the former is first coveredand then uncovered by .,the mass 'of medium, thereby leaving on thesurface a layer of medium which, when dry, provides with the former acompositetube with a smooth surface. The relative movement between theformer and the mass of medium may be effected by immersing the former inthe mass or by forcing the liquidupwards in contact with the former orby. al- I lowing the medium to run downwardsunder the action of gravityin contact-with the former.

cordingly, there is no-mandrel to prevent the medium from beingdeposited on the inner wall ofthe former. It is, in fact, particularlyadvantageous to build up the liquid medium 'on the inner wall or a'former, when'the latter is made of textile material and the tube isto-be used for conveying gasoline to an engine, because the innercoating prevents the carburetterjets of the engine being choked by fiuifpicked up from the former by. the gasoline.

Yet another object ofthe invention consists in a flexible tube, the wallof which comprises a tubular mass of material, such as polyvinylalcohol, and an infiernal reinforcement of braided metal wire gauze. Abraided metal wire former readily retains its pre-forined shape withoutany internal support along its length. Further, a braided wire former offairly open mesh has the advantage that, when it is coated bothinternally and externally, with the liquid medium, the inner I sible inrelation to the thickness of the tube wall,

the finished tube consists mainly of 'th medium I withonly sufllcientwire braid to ma tain its The invention particularly aims at providing astrong pliable tube with a smooth bore. Thus, anotherobject of theinvention is the method of manufacturing a flexible tube which includesthe step of setting up relative reciprocating motion between apre-formed braided or woven a mass of liquid medium within the former tocover the inner surface of the former and then to uncover that'surface.leaving on-' the surface a layer of medium which. when dry, provideswith the former a composite tube having a smooth bore.

Owing to the fact that a pre-formed tubular form er will retain itsshape without any internal mandrel, the former may be supported withoutthe use of such a mandrel during the building up of the liquid mediumonthe former. Ac-

form and the natural flexibility of the medium appears in the flnishedtube. Inthe case of a metal former made of open mesh braiding, with eachinterstice substantially in the form of a square havinga side ofone-sixteenth'of an inch, the interstices being covered only with a fllmof polyvinyl alcohol, it has been found that-the tube will withstand apressure as high as 200 lbs. per square inch. The metal wires of whichthe braiding is formed may be either single wires. or

composite wires in the form of flat strips consisting of a number-o1wires side by side in contact with each other. i

It is preferable for the with its axis vertical or, substantiallyvertical when undergoing treatment with the coating medium. i

In carrying the invention into effect, it is usually desirable to givethetubular former successiv'e treatments with the medium andto dry thetube after each treatment so that a coating of the dried medium is builtup layer by layer on the inner or outer surface or both. when thepre-for'med. tubular former. is made of braided or woven material, theinvention enables I a smooth bored. tube to be produced which not formerto be supported 1 application of the varnish.

only renders the tube impervious to the fluid,

' but also greatly reduces the skin friction.

When the relative movement between the flexi ble former of tubular formand the coating medium is effected by dipping the tube in'the mebe usedas coating mediums. with man; rms 'of synthetic resin, it is desirableto add a plasdium, it is convenient to arrange for a batch of formers,disposed side byside with their axes vertical, to be dipped in a wellfrom which the batch is subsequently withdrawn for removal to a dryingchamber. In "an alternative arrangement, a pre-formedtubular former isheld vertically while a quantity of the liquid medium is pumped upwardsinside or outside the former and then allowed to recede so as to leave alayer of the medium deposited on the inner or outer ticising agent. Themediums may have fillers introduced such as metallic powders or asbestosfibre.

The tubular formers employed may, as iridicated above, be formed bybraiding or weaving, in which casemetal, paper or textile threads may beused. Alternatively, the former may consist of a rubber hose or aflexible metallic tubing. When the material of the former is such thatit will not'readily maintain its shape, it may be treated with astiffening material. Thus, thin cotton braid may be stiffened by starchor wax to enwall of the'former, the layer being subsequently dried. Theliquidmedium, after reaching the top of the former, may be allowed tospill over the upper edge of the former and run down the other 'sideofthe former so that both surfaces are coated with a layer of the medium.When the medium is pumped upwards outside the former and then allowed torecede, the former has to'be mounted in a' chamber, and may be sosupported in the chamber that the medium rises and falls simultaneouslyboth inside andoutside sure the, shape of the former being maintainedduring the coating process.

A great variety of shapes or forms of tubular formers maybe used incarrying out the invention which, unlike those processes in which fapipe is coated as it is formed on a loom or braiding machine, is notlimited to the manufacture of simple cylindrical pipes or tubes butnot'only ent ables tubes of any desired cross-section to be' made butenables the cross section to vary along the length of the tube whileyetthe tube hasthe former to cover both its surfaces with the medium.

In all the methods according to the invention,

the viscosity of the medium may be controlled and the number of coatsneeded for any given thickness of tube wall can be selected at will.The, medium may be heated and the pre-formed former maybe given apreliminary coating" of medium which is less dense than thesubsequentthe surface to be coated, and is particularly useful when the tubularformer is of metal braid. Other forms of'preliminary treatment may be'necessary. For example, when galvanised steel wire braid is to be coatedwith asynthetic resin varnish, good adhesion of the varnish to the zinccoating of the wire may be obtained if the braid' is subjected to adipping treatment prior to the Additional coatings of different kindsmay beapplied selectively to the tubular former. Thus, the formerf'mayfirst have its inner surface or,

solution of polyvinyl alcohol is the liq final coating of paint or amedium containing a; metallic powder so as to give the appearance ofboth its inner and outer surfaces coated with a medium that is wellsuited to resist the mud which the finished tube will have to carry.Then, a medium which is cheaper or more suited to withstand the externalconditions #59 which the finished tube is to be subjected, may beapplied to the outer surface only, means'being provided for stopping thefiow'of medium inside the tubular former. v

The properties of the mediums used must be tic, when dry. They'must alsobe resistant to the liquid or gas to be handled bythe finished in andposses goodageing properties. In some 5 cases, also, the mediums may becalled upon to resist high temperatures. 1 5 rubbersolutions, syntheticrubbers in sol1ition,- and-solutions 'of synthetic resins, particularlysoi lutiops of polyvinyl alcohol or its derivatives, may

Cellulose lacquers,

I such that they are flexible, and preferably'elasa smooth bore.

' In certain circumstances, the coating medium" may have to be subjectedto a hardening treats ment, and in thiscase, the built-up tube mayhave'to be immersed in a bath of some hardening solution or thishardening solution may be cir-. culated through the tube. As an exam 1e,if a employed, it maybe hardened by'immersion in a bath of formaldehyde.Usually, however, the hardening is performed by placi g the coated tubein an oven. ordinary drying, as with hot air, it is very important thatthe inner surface of the tube shall medium In this case and in thecaseof be adequately-treated. The treatmentjof the mner surface is bestefiected by circulating heated air through the tube. g

' The outer surface of the tube may-be given a metal. .Alternatively,the tube may be given a protective covering such as a' lapping of tape,a woven or braided covering of wi e or textile yarn, or a rubbercovering. I

From the foregoing remarks it -.will be seen that the invention'isconcerned with the building up of a tube from a liquid medium upon aformer which remains part of the finished tube. It may be employed inmaking tubes of any desired crosssection and of uniform or varyingcross-section along its length. Furthermore, the invention" .providestubes of increased strength due to the reinforcement or alternatively itprovidesa tube of given strength with less,material and this re-" ducesproduction costs.

In order that the invention may be clearly understood and readilycarried into effect, vari? ous methods and apparatus for use in carryingout those methods will now be described, by way of example, withreference to the accompanying drawings, in which: I

Figure 1 is aside elevation of one apparatus,

partly in section;

Figure 2 is an end elevation of "apparatus, part- I v .ly in section,for use in conjunction with the apparatus of Figure 1;

Figure 3 is a'sectional elevation to an enlarged scale of a detail ofFigure 2;

Figure 4 is a diagrammatic illustration of an apparatus for-drying thefinished tubes by suck- Figure 7 is a side elevation, on a larger scale,

of an assembly, partly in section, as used in the apparatus of Figures 1and 2;

Figure 8 is a sectional plan of the assembly of Figure '7;

Figures 9 and 10 are respectively part-sectional and sectionalelevations showing ways in which the assembly of Figures 7 and 8 can bemodified.

Figure 11 is a part sectional elevation of part of a further modifiedversion of the assembly of Figures '7 and 8;

Figures 12 and 13 are sectional elevations of modifications of'the partshown in Figure 11;

Figure 14 is a side elevation of a further form of apparatus, partly insection;

Figure 15 is a view similar to Figure 14 but with some of the parts indifferent positions;

Figure 16 is a sectional side elevation of another form of apparatus;

Figure 17 is a sectional side elevation of yet another form ofapparatus;

Figures 18 and 19 are sectional side elevations of modifications of theapparatus in Figure 17;

and

Figure 20 is an elevation of part of a braided tube, partly in section.

In using the apparatus of Figure 1, a number of pre-formed formers I oftubular form, to be coated by dipping, are arranged vertically be-. I

tween two frames 2 and 3, the assembly being suspended either-from ahook 4, fixed to an overhead conveyor 5, or, as shown in' Figure 1, froma hook 6, at one end of a cable]! passing over a pulley 8, on theconveyor, and a pulley 9 to electrically-driven lowering and liftinggear A."

When the nest of formers ls,on the hook 6, the conveyor 5 is fixed inposition for the assembly to be lowered into a dipping well Ill, threeof which are shown in Figure 1. The lowering gear illustrateddiagrammatically in Figure 1, includes a large winding d m a driven froman electric motor I) through reduction gearing c and belting (1. Themotor I) is switched on by hand so.

After immersion,'the former assembly is removed from the hook 6 and hungon the hook L- The conveyor 5 isthen run along an overhead rail II to adrying chamber or oven shown in Figure 2. After drying, the formerassembly may be returned to the dipping wells III for a furtherimmersion to increase the thickness of the coating. The number ofimmersions and intermediate drying treatments depends, of course, on thenature of the coating medium and upon the thickness of the wallrequired. The apparatus lends itself to the simultaneous treatment of anumber of former assemblies, in which case the assemblies are loweredsimultaneously into their respective wells and withdrawn simultaneouslyfrom the wells, subsequently being taken to the drying chamber. to betreated simultaneously therein. The former assembly, or each assembly,may be dipped first in one well containing a thin solution of thecoating medium or another liquid, such as water or spirit, which servesto wet the surfaces of the formers thereby facilitating the fiow of thecoating medium over their surfaces when the formers are dipped in asecond well containing the coating medium proper. If necessary, thewells may be "provided with heating jackets, the right hand well Ill inFigure 1 being shown with such a jacket I2.

Water or oil may be circulated through the jacket I2 by means of a pumpI3, the circuit including a heater I4. A ball cock I5, controlling anoverflow pipe I6, is mounted at the upper end of the jacket I2 so as tocontrol the level of liquid therein. In some circumstances, it may befound desirable to circulate steam through the jacket instead of aliquid. Surface discs H are put to fioat on the medium in the wells soas to keep the medium clean and prevent surface oxidation when themedium is not in use.

The drying chamber or oven shown in Figure 2 has walls I8 lagged withheat-insulating material and a floor I9 formed with hot air ports 20which can be selectively opened and closed by means of sliding'valveplates 2|. In Figure 2,

that the drum 0. rotates,to lower the nest of tubular formers I into theclipping chamber or well Ill. When the formers I are submerged to therequired depth, an adjustable tappet e on the rim of the drum aautomatically opens the motor switch I and starts a solenoid time theleft hand floor ports 20 are shown closed by their respective valveplate 2I,'whi1e the right hand floor ports are shown open, the righthand valve plate 2| being in its retracted position. As n, there are aset of three air ports 20, 20a

ri -ending to each tubular former I, the centre iiple 20a, beingsufficiently large to allow the nozzle plug 34 to enter it when theformer assembly is lowered to a sufficient extent as seen switch, whichafter a. predetermined time for which it is set, starts the motor bagain in the opposite direction, thereby raising the nest of formers Ifrom-the chamber I0. 7

A second adjustable tappet g on the drum a switches off the motor 12when the formers I are fully withdrawn. The tubular formers are steadilyimmersed at a predetermined rate. This.

eliminates the risk of air being entrained and of the medium beingdisturbed during the movequired, the electrically-driven gear may bereplaced by hand-operated tackle.

in Figure 3. The smaller holes 20 merely admit the heated air for dryingthe outside surfaces of the tubes I. This arrangement makes the passageof heated air through the inside of the tubes more certain and, in fact,the provision of the smaller holes 20 is not very important as the air'ment of the nest of formers within a dipping well.

,The correct timing of the immersion and withv in the oven may bemaintained at the desired temperature merely by leakage from the largeholes 20a into the oven. The hot air is thus directed, by being causedto-pass through the right hand ports, on to the former assembly hangingimmediately above these-ports. The air, after passing over the formers,is discharged through a chimney 22 at the upper. end of the chamber. Thedrying air is drawn through a funnel 23 by a fan 24 and delivered firstthrough a heater 25 and then through a pipe 26 .to a manifold 21, fromwhich the-ports 20 lead.

It is often found preferable, instead of blowing the heated air upthrough the tubes as described with reference to Figures 2 and 3, tosuck the air up throughthe tubes I. The reason is that it leaves thebottoms of the tubes I free to drip. Then, of course, it is notnecessary to leave the tubes I so long over the tanks I8 (Figure l) todrip since drying can take place in the drying oven before the coatingof liquid medium has "much chance to run.

One form of suitable apparatus for purpose is shown in Figure 4. The topplate I5 of the frame is.provided with a reasonably air-tight cover I6which has an air pipe 11 through which air can be drawn. The air pipe 11is connected to an air suction trunk 18 by a removable flexible tube19.. The branches 11, I9 when not in use are shut off by means of cocks80. The air trunk "I8 is connected to the suction inlet of the air Ipump 24 by an inlet pipe 8|, the air passingv through the heater 25 andpipe 26 into the oven.

. A further development of the suction method of drying suitable for usewhen rectangular wells are employed for the liquid medium is illuse andlower frames are shown. The lower end of the tubular former I'is securedto abush 33 by means of a plug 38 which, unlikethev plugs 34 in Figure3, has no axial bore, so that the formerI will only be coated on theexternal surface. The upper end of the former I in Figure 8 is slippedon to the external conical surface of a member 38 which is connected toa plate,'

- clipped on to the conical external surface of a trated in Figures 5and 6. The tubular formers v I 'to be dipped are arranged in a straightrow; This enables the top member 16 of thedipping frame to be made as atube with the air pipe 11 leaving at the end.

The frames 2 and 3, between which the formers I extend, may take theform shown in Figures 7 and 8. Inthis case, only the lower frame isarranged for immersion, the upper frame consisting simply of a disc 28formdwith apertures 29 and carrying a ring 30 for receiving one of thehooks 4 or 6. The lower frame is designed to create but littledisturbance of the medium, as the assembly is immersed, and is designedso that its total surface area is small and so thatits surfaces prevent,as far as possible; any adhesion of the medium used. This lower frame,

which is connected rigidly to the upper frame by a central rod 3|,consists of a network of plates 32. The depths of these plates areconsiderable in relation to their cross-sections which'are of streamlineform. At Various points in the netupper ends of the formers I-areslipped over conical surfaces formed externally on members 36 .which arepushed into the apertures 29 in the,

plate 28. These members 36' are formed with axial bores 31 for the inletand outlet of air as the coating medium passes up and down within theformers I. In the drying operation, the bores 85 in the plugs 34 and thebores 31 in the members 36 permit the drying air to pass through theformers .I.

In some cases where fairly short tubular formera are .to be coated, anintermediate frame may be provided between the upper and lower frames.Two batches of formers, one between the upper frame and the intermediateframe, and the other between the intermediate frame and the lower frame,can then be treated simultaneouslyn some cases, it is desirable toreverse the assembly between each'dipping operation. In those cases,

the. upper and lower frames are of similar design Theformers I areclamped within the.

member 4|, screwed into a plate similar to the plate 28 in.Figure 7. Itwill be appreciated that, when the formers I are secured at their endsto members that are detachably mounted on the upper and lower frame,various sizes of former may be accommodated between the same pair offrames by providing members, such as the members 40 and H, correspondingto the sizes of the formers. These members 48 and 4| may, in fact,

be regarded as adaptors formertobe used. a

The rod 3| (Figures 7 and 8) may be dispensed with if the lower frame issufficiently suited to the size of the heavy to keep the formersstraight. In the case a of braided tubular formers, however, the'lowerframe must not be so heavy as to cause a substantial change in thecross-section dimensions 7 of the formers. The weighted frame mayconsist of a ,spider having a streamline weightat the end of each limb.Such weights may fit into and provide the connections between theformers and the frame. One such weight 42 is shown in Fig-- ure 11. thatonly the outside of the former will be coated. If both surfaces of theformer are to be coated,

' the weight can be provided with an-internal bore, as shown in Figure12, which also shows the provision of a clip .43 for pressing the wallof the former into an annular groove on the outer surface of the weightso that the parts are more securely joined than when friction alone isrelied upon. The weight may, as shown in Figure 13, be. provided with aninternal bore that is conical in form at its lower end. A conical plug44 may be inserted into the lower end of the bore at any time in thedipping process when it is desired that onlythe outside surface of theformer shall dium is forced upwards therein but is not allowed' and areboth arranged forv attachment to the hooks 4 and} (Figure l).

In "Figure 9, modified ways of securing the upper and lower ends of atube I to the upper When the lower frame is a. spider, having weights,as shown inc Figures 11, 12 and'l3, at the ends of its limbs, the lattermay be hinged relatively to each other so as to allow' for variations inthe lengths of the formers.

Figure 14 shows an arrangement for building up a coating on a tubularformer l by forcing the coating medium up inside the former and thenallowing themedium to recede. The medium is supplied through a pipe 45,which is con- 1 to run over the top of the former. The medium is thenallowed to recede. The parts of the bayonet joint are then separated anda hood 48 is swung the position shown in Figure 15, in

In this case, the arrangement is such 45 again connected to the nozzle45 so that the second internal coating may .be applied to the former I.In the case where it is required to coat both sides'of the tubularformer I, the medium may be forced up inside the former to the topthereof so that it spills over the upper end of the former and runs downthe outer surface thereof, as shown by the'arrows in Figure 14, thesurplus medium being received in a funnel 50. In the drying process, thehot air, delivered through the hood 49, passes upwards both inside andoutside the former I, so that the drying takes place simultaneously onboth sides of the wall of the former.

It will be appreciatedthat' an apparatus as shown in Figures 14 and 15can be arranged to allow a number of formers to be treatedsimultaneously and in parallel in the same chamber 48, by providing anumber of nozzles 45 and pipes 45. v

Figure 16 shows a somewhat similar arrangement in which a tubular formerI, to be coated, is suspended at its upper end by a wire loop and titsat its lower end over a nozzle 52. Awire loop, similar to the loop 5|,may be used in the apparatus of Figure 14 for supporting the upper endof the former I in that figure. In Figure 16, a submerged pump 53delivers coating medium from a tank 54 upwards through the nozzle '52.After overflowing at the upper end of the former I, the medium runs downthe outside thereof and returns through a funnel 55 to the tank 54.After surfaces of the chamber are subjected, may be such as greatly toreduce or completely to prevent the tendency for the coating medium toadhere to the inside of the chamber 59.-For

example, the latter may be tinned and polished internally.

The apparatus in Figure 17 may be-modirled as shown in Figure 18,thelowerend of the tubular former I 'to be coated being fitted directlyto a nozzle I0, so that the medium, instead of flowing simultaneouslyupwards both inside and outside the former I, flows upwards only insidethe former I. After reaching the topof the latter, the mediumoverfiows'and runs downwards outside the former I, leaving an externalcoating. Figure 19 shows a modification of the arrangement in Figure 18,in which the medium can only be passed up and down inside the former I.In this case, a sight glass II is mounted at a predetermined time, thepump 53 is stopped tank 54 through a spout 15, the medium, as itrecedes, leaving the desired coating within the former I. Naturally, ifonly the inside of the former is to be coated, the medium is notpermitted to spill over the top of the former.

In the apparatus of Figure 1'7, a tubular former I, to be coated, islocated between nozzles 51 and 55 within a chamber 59. To bring thecoating medium into contact with the former I, compressed air isadmitted through a valve 50 and pipe 5| to a tank 52 containing themedium, while an exhaust valve 58 and a hot air valve 59 are closed. Themedium is thus forced upwards through'a pipe 53, a valve 54, and a sightglass 55 to the chamber 59. The medium passes upwards through thechamber, both inside and outside the, former I, and, as the mediumrises,

air is exhausted from inside the former I and.

from inside the chamber through conduits 55 and 51. After rising in thechamber 59', the medium is allowed to recede as a result of the closingof the valve 5 andthe opening of the rangement, it is. necessary toprevent a thick layer of the medium from gradually building up on thewalls of the chamber 59. Accordingly, a

' scraper, that is operated after each passage of the medium intothechamber 59, may be provided in the latter.

1 of the material irom which the chamber 55 is made-or a surfacetreatment to which the inside 75 Alternatively, the naturethe upper end01 the former I, so that the operator can see when sufficient medium hasbeen admitted. -When the former I is a braided tubular member, some ofthe medium may ooze through the braided wall and run down the outside ofthe former, leaving an external coating.

In the arrangements shown in Figures 18 and 19, an external chamber likethe chamber .59 in Figure 1'7 is .unnecessary, although this mayadvantageously be provided in the construction of Figure 18 when thetube isto be dried in situ in the manner described with reference toFigure 1'7. When applied to the arrangement of Figure 18, the chamber.would not be liable to receive a coating of medium on its walls.

of the external chambers, the constructions. shown in Figures 18 and 19are provided with I trays '12, having drain pipes 13, for collectinganymediumthat runs down the outsides of the formers,

The foregoing methods and apparatus need not necessarily be used formaking simple cylindrical tubes, but they may be adapted'to theformation of, tubes having irregular cross-sections. The braided formerof tapered shape shown in Figure 20, for example, may be used inaccordance with the invention. The invention is also suited to thecoating of pre-formed tubular formers having integral flanges'at rightangles to their axes. Such formers, having integral flanges, are usefulinpi'actice in that they may be connected directly .to adjacent parts.This is particularly helpful in the aircraft industry where joints haveto be made between tubes and tanks having such thin walls thatcomparatively heavy unions are impracticable.

When, as is usually the case in carrying out the invention, the tubularformer is given a number of coats, it is desirable to allow time for themedium to flow into an even coating between each treatment with themedium and prior to pressures may be formed by incorporating two or moreconcentric pre-formed tubular formers in the tube. Thus, a braidedtubular former may be treated with the medium in any of the man-- nersset out above and dried after the application of each layer. Theresulting tube ispassed through a braiding machine and thus anotherlayer of braiding is tightly applied to the outside- In the absencedrying effected after applying each layer.

sired, and finally the tube is provided with ex'- ternal coatings of theliquid medium with drying as already described.

When the pre-formed former is coated by IOl'C-r ingthe medium-upwardsand allowing it to recede, as described, for example, with reference toFigure 17, it is not necessaryfor the tubes to be dried in situ. Anumber of tubular formers may, in fact, be-arranged between frames inthe manner described with reference to Figure 1, the assembly beingfirst put in a chamber arranged like the chamber 68 in Figure 17 andthen removed to a drying chamber like that shown in Figure 2.

I claim: The method of manufacturing .a flexible elastic tube or hosecapable of withstanding extremely high pressure and resistant to theaction of gasoline, which consists of the steps of making a braidedtubular former, coating the inside and outside of said former byrepeated relative dipping actions with a polyvinyl alcohol resin, a1-

10 lowing the resin to dry between each dipping action, superimposinganother braided former tightly on the outside of said partiallyformedtube, and applying further layers (if said resin to the outside of saidtube in the same manner until 15 the desired strength and size areobtained.

HORACE GRINT.

